The twin screw extruder has the extruder principle of a single screw extruder: solid conveying, melt boosting, and pumping, mixed stripping and devolatilization, but this is not simply the case. The research on twin screw extrusion theory started late, coupled with its diverse types, complex screw geometry, and complex extrusion process, which brings many difficulties to the research.

Overall, the research on twin-screw extrusion theory is still in its initial stage, which is known as' skill surpasses science '. The study of its extrusion process can be roughly divided into three stages:

1. The law of changes in the physical state of polymers during the extrusion process, the principle of transportation, and the truth and law of solid melt transportation and exhaust, establish a mathematical and physical model to guide the design of twin screw extruders and the optimization of the extrusion process.

2. It is necessary to understand the true state changes, mixing morphology, structural changes, and the relationship between the final mixture and performance of two or more polymers and materials during the extrusion process.

3. As a twin screw extruder, the internal relationship between the reaction process, speed, performance, screw configuration, and operating conditions during extrusion reaction molding is established to guide reaction molding extrusion.

The development of twin screw extruder: It was first successfully developed in Italy in the 1930s and developed rapidly in the late 1960s and early 1970s. With the development of RPVC products and polymer modification, the co directional twin screw extrusion theory cannot adapt to the development of applications, forming a consensus worldwide and becoming a research hotspot.